Preactivated thiomers as mucoadhesive polymers for drug delivery

This study was aimed to synthesize polymeric excipients with improved mucoadhesive, cohesive and in situ-gelling properties to assure a prolonged retention time of dosage forms at a given target site, thereby achieving an increased uptake and improved oral bioavailability of certain challenging therapeutic agents such as peptides and proteins. Accordingly, poly(acrylic acid)-cysteine-2-mercaptonicotinic acid (PAA-cys-2MNA) conjugates were synthesized by the oxidative S-S coupling of PAA-cys (100-, 250- and 450 kDa) with 2-mercaptonicotinic acid (2MNA). Unmodified PAAs, PAAs-cys (thiomers) and PAA-cys-2MNA (100-, 250- and 450 kDa) conjugates were compressed into tablets to perform disintegration tests, mucoadhesion studies and rheological measurements. Moreover, cytotoxicty of the polymers was determined using Caco-2 cells. The resulting PAA-cys-2MNA (100-, 250- and 450 kDa) conjugates displayed 113.5 ± 12.7, 122.7 ± 12.2 and 117.3 ± 4.6 μmol/g of 2-mercaptonicotinic acid, respectively. Due to the immobilization of 2MNA, the PAA-cys-2MNA (pre-activated thiomers) conjugates exhibit comparatively higher swelling properties and disintegration time to the corresponding unmodified and thiolated polymers. On the rotating cylinder, tablets based on PAA-cys-2MNA (100-, 250- and 450 kDa) conjugates displayed 5.0-, 5.4- and 960-fold improved mucoadhesion time in comparison to the corresponding unmodified PAAs. Results achieved from tensile studies were found in good agreement with the results obtained by rotating cylinder method. The apparent viscosity of PAA-cys-2MNA (100-, 250- and 450 kDa) conjugates was improved 1.6-, 2.5- and 206.2-fold, respectively, in comparison to the corresponding unmodified PAAs. Moreover, pre-activated thiomers/mucin mixtures showed a time dependent increase in viscosity up to 24 h, leading to 7.0-, 18.9- and 2678-fold increased viscosity in comparison to unmodified PAAs (100-, 250- and 450 kDa), respectively. All polymers were found non-toxic over Caco-2 cells. Thus, on the basis of achieved results the pre-activated thiomers seem to represent a promising generation of mucoadhesive polymers which are safe to use for prolonged residence time of drug delivery systems to target various mucosa.     

Biosoluble polymers for drug delivery

The immobilization of α-chymotrypsin on periodate oxidized cellulose as a biocompatible carrier was investigated. The properties and release of the enzyme from the polymer were studied. It was found that after an initial spurt, the amount of the released enzyme attains a practically constant value and the released enzyme retains its activity and shows increased heat stability. Such systems may be useful for a slow delivery of drugs and enzymes in the body.     

Biamphiphilic triblock copolymer micelles as a multifunctional platform for anticancer drug delivery

Novel micelles from biamphiphilic triblock copolymer poly(ethylene glycol)-b-poly(ε-caprolactone)-b-poly(acrylic acid) (PEG-b-PCL-b-PAA) as new multifunctional nanocarriers to delivery anticancer drugs were evaluated. The well-defined triblock copolymers prepared by controlled polymerizations self-assembled into micelles in aqueous solution with a hydrodynamic radius of 13 nm as obtained by dynamic light scattering (DLS) and a low critical micellization concentration of 2.9 × 10(-4) g/L. The hydrophobic PCL cores of micelles were applied to load hydrophobic drug doxorubicin and the functional PAA subcoronas clung to the micellar core were used to carry cisplatin through covalent interaction. The results indicated that two anticancer drugs had been loaded by different mechanism either separately or simultaneously. Drug loading content and efficiency as well as release profiles were evaluated. Furthermore, internalization and cytotoxicity of the anticancer nanoparticles against human bladder carcinoma EJ cells were studied. The biamphiphilic triblock copolymer micelles provided not only biocompatibility and biodegradability, but also abilities for loading single and dual anticancer drugs, indicating that this was a useful multifunctional platform for anticancer drug delivery.     

Polyglycerol-coated nanodiamond as a macrophage-evading platform for selective drug delivery in cancer cells

A successful targeted drug delivery device for cancer chemotherapy should ideally be able to avoid non-specific uptake by nonmalignant cells, particularly the scavenging monocyte-macrophage system as well as targeting efficacy to bring the drug preferentially into tumor cells. To this purpose, we developed a platform based on detonation nanodiamond (dND) with hyperbranched polyglycerol (PG) coating (dND-PG). dND-PG was first demonstrated to evade non-specific cell uptake, particularly by macrophages (U937). RGD targeting peptide was then conjugated to dND-PG through multistep organic transformations to yield dND-PG-RGD that still evaded macrophage uptake but was preferentially taken up by targeted A549 cancer cells (expressing RGD peptide receptors). dND-PG and dND-PG-RGD showed good aqueous solubility and cytocompatibitlity. Subsequently, the anticancer agent doxorubicin (DOX) was loaded through acid-labile hydrazone linkage to yield dND-PG-DOX and dND-PG-RGD-DOX. Their cellular uptake and cytotoxicity were compared against DOX in A549 cells and U937 macrophages. It was found that dND-PG-DOX uptake was substantially reduced, displaying little toxicity in either type of cells by virtue of PG coating, whereas dND-PG-RGD-DOX exerted selective toxicity to A549 cells over U937 macrophages that are otherwise highly sensitive to DOX. Finally, dND-PG was demonstrated to have little influence on U937 macrophage cell functions, except for a slight increase of TNF-α production in resting U937 macrophages. dND-PG is a promising drug carrier for realization of highly selective drug delivery in tumor cells through specific uptake mechanisms, with minimum uptake in and influence on macrophages.     

Novel fluorescent copolyanhydrides as potential visible matrices for drug delivery

Two classes of fluorescent copolyanhydrides were synthesized by melt copolycondensation of the fluorophoric diacid, p-(carboxyethylformamido)benzoic acid (CEFB), with sebacic acid (SA) or N-trimellitylimidoglycine (TMA-gly). Alternate copolyanhydride based on SA and CEFB was also prepared by solution polycondensation of CEFB and sebacoyl chloride. 'H NMR spectra of the copolymers confirm their structures. Fluorescence was observed for all the copolymers, the intensity of which increases with the CEFB fraction. Either blue (ca. 429 nm) or green (ca. 520 nm) light can be emitted from the copolymers with the excitation of UV (356 nm) and visible (470 nm) light, respectively. The polymers were further fabricated to microsphere formulation, which can be clearly visualized by fluorescent microscopy.     

Novel PCL-based honeycomb scaffolds as drug delivery systems for rhBMP-2

This study investigated a novel drug delivery system (DDS), consisting of polycaprolactone (PCL) or polycaprolactone 20% tricalcium phosphate (PCL-TCP) biodegradable scaffolds, fibrin Tisseel sealant and recombinant bone morphogenetic protein-2 (rhBMP-2) for bone regeneration. PCL and PCL-TCP-fibrin composites displayed a loading efficiency of 70% and 43%, respectively. Fluorescence and scanning electron microscopy revealed sparse clumps of rhBMP-2 particles, non-uniformly distributed on the rods' surface of PCL-fibrin composites. In contrast, individual rhBMP-2 particles were evident and uniformly distributed on the rods' surface of the PCL-TCP-fibrin composites. PCL-fibrin composites loaded with 10 and 20 microg/ml rhBMP-2 demonstrated a triphasic release profile as quantified by an enzyme-linked immunosorbent assay (ELISA). This consisted of burst releases at 2 h, and days 7 and 16. A biphasic release profile was observed for PCL-TCP-fibrin composites loaded with 10 microg/ml rhBMP-2, consisting of burst releases at 2 h and day 14. PCL-TCP-fibrin composites loaded with 20 microg/ml rhBMP-2 showed a tri-phasic release profile, consisting of burst releases at 2 h, and days 10 and 21. We conclude that the addition of TCP caused a delay in rhBMP-2 release. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and alkaline phosphatase assay verified the stability and bioactivity of eluted rhBMP-2 at all time points.     

Bioadhesive polymers in peptide drug delivery

A frequently encountered problem with the peptide-based drugs which are becoming available is that these agents must generally be administered by injection. There is therefore considerable research interest in alternative delivery routes, such as the buccal and nasal mucosae, and the conjunctiva. This paper reports some quantitative considerations of peptide delivery via the buccal, nasal, ocular and gastrointestinal routes, based on estimates of permeability coefficients and other necessary parameters. Rates of delivery and the resulting systemic levels are calculated for some peptide drugs, and compared to therapeutic levels: situations are identified in which bioadhesive formulations may be of benefit.     

Brain drug delivery and neurodegenerative diseases: Polymeric PLGA-based nanoparticles as a forefront platform

The discovery of effective drugs for the treatment of neurodegenerative disorders (NDs) is a deadlock. Due to their complex etiology and high heterogeneity, progresses in the development of novel NDs therapies have been slow, raising social/economic and medical concerns. Nanotechnology and nanomedicine evolved exponentially in recent years and presented a panoply of tools projected to improve diagnosis and treatment. Drug-loaded nanosystems, particularly nanoparticles (NPs), were successfully used to address numerous drug glitches, such as efficacy, bioavailability and safety. Polymeric nanoparticles (PNPs), mainly based on polylactic-co-glycolic acid (PLGA), have been already validated and approved for the treatment of cancer, neurologic dysfunctions and hormonal-related diseases. Despite promising no PNPs-based therapy for neurodegenerative disorders is available up to date. To stimulate the research in the area the studies performed so far with polylactic-co-glycolic acid (PLGA) nanoparticles as well as the techniques aimed to improve PNPs BBB permeability and drug targeting were revised. Bearing in mind NDs pharmacological therapy landscape huge efforts must be done in finding new therapeutic solutions along with the translation of the most promising results to the clinic, which hopefully will converge in the development of effective drugs in a foreseeable future.     

Polyampholyte polymers as a versatile zwitterionic biomaterial platform

Polyampholyte polymers are a subclass of zwitterionic materials that are composed of mixtures of charged monomer subunits. These materials have properties that mimic those of the more widely characterized zwitterionic polymers as long as their polymer chemistry has been well controlled. In particular, overall neutral polyampholyte polymers have been shown to have resistance to nonspecific protein adsorption and protein conjugation capability. This has been demonstrated for both polymer brush and hydrogel-based platforms. In this review, our recent work demonstrating these characteristics will be summarized and placed into the broader context of zwitterionic materials.     

A conductive nanostructured polymer electrodeposited on titanium as a controllable, local drug delivery platform

Infection and inflammation associated with orthopedic implants can be life threatening, time consuming, and expensive, thus, motivating the development of a local drug delivery platform that could prevent such deleterious events. For this purpose, nanostructured polypyrrole (PPy) incorporating antibiotics and anti-inflammatory drugs (penicillin/streptomycin (P/S) or dexamethasone (Dex), respectively) were coated on commercially pure titanium through an easy to use electrochemical deposition method. As shown in our previous study, about 80% (compared with initial amount) of these incorporated drugs were released after electrical stimulation spanning five cycles (voltage was varied between -1 V and 1 V). In a further continuation of this work, nanostructured P/S incorporated PPy coatings on titanium were demonstrated to be bactericidal against Staphylococcus epidermis after 1 h, and when incorporated with Dex, inhibited macrophage (an inflammatory and immune response cell) growth after 8 and 13 h of in vitro culture. Moreover, nanostructured PPy-drug films coated on titanium enhanced osteoblast (bone forming cells) proliferation, while at the same time, suppressed fibroblast (fibrous tissue forming cells) proliferation for up to 5 days. After electrical stimulation, antimicrobial and anti-inflammatory-coated devices yielded lower bacteria colonies and macrophage growth compared with unincorporated-drug PPy films (controls). This study, thus, suggests that drug incorporated nanostructured PPy coatings on titanium are capable of effectively treating potential orthopedic implant infection and inflammation, and lays the foundation for the further development of local and controllable on-demand drug delivery coatings to improve orthopedic implant efficacy.     

Platinum (IV)-coordinate polymers as intracellular reduction-responsive backbone-type conjugates for cancer drug delivery

Platinum (IV)-coordinate polymers were synthesized by condensation polymerization using diamminedichlorodihydroxyplatinum (DHP) or its dicarboxyl derivative diamminedichlorodisuccinatoplatinum (DSP) as comonomers. Cyclic voltammogram study showed that Pt (IV) in the polymers was much easier reduced to Pt (II), particularly at the acidic pH, than that in the monomer DSP. Thus, these polymers were intracellular reduction-responsive backbone-type polymer conjugates that could be degraded and release Pt (II). These conjugates not only had high and fixed platinum contents (27.7% for P(DSP-EDA) and 29.6% for P(DSP-PA), respectively), but also showed increased cytotoxicity compared with corresponding Pt (IV) monomer DSP toward various tumor cell lines. In vivo, the conjugate showed a longer blood circulation time and better tumor accumulation.     

Novel carboxymethylcellulose-based microporous hydrogels suitable for drug delivery

Several materials capable of acting as structures for controlled release were analysed for the fabrication of matrices. Among those used, hydrophilic polysaccharides appeared to be the most suitable materials. Carboxymethylcellulose (a semi-synthetic polysaccharide) was chemically cross-linked with a 60% and 90% cross-linking degree in order to obtain hydrogels and utilised as matrix for the realisation of controlled drug release systems. The morphology of the gels was changed in order to obtain a microporous structure with different porosity (14, 30 and 40 μm). The obtained porous matrices were characterised in terms of pore density, dimension and swelling behaviour. The influence of both the pore dimension and technique of loading on the release kinetics was analysed. By increasing the pore dimension the release of ibuprofen-lysin was slower. Inducing the microporous structure after the loading of the hydrogel with the drug resulted in a slower release.     

Novel carboxymethylcellulose-based microporous hydrogels suitable for drug delivery

Several materials capable of acting as structures for controlled release were analysed for the fabrication of matrices. Among those used, hydrophilic polysaccharides appeared to be the most suitable materials. Carboxymethylcellulose (a semi-synthetic polysaccharide) was chemically cross-linked with a 60% and 90% cross-linking degree in order to obtain hydrogels and utilised as matrix for the realisation of controlled drug release systems. The morphology of the gels was changed in order to obtain a microporous structure with different porosity (14, 30 and 40 microm). The obtained porous matrices were characterised in terms of pore density, dimension and swelling behaviour. The influence of both the pore dimension and technique of loading on the release kinetics was analysed. By increasing the pore dimension the release of ibuprofen-lysin was slower. Inducing the microporous structure after the loading of the hydrogel with the drug resulted in a slower release.     

A smart polymeric platform for multistage nucleus-targeted anticancer drug delivery

Tumor cell nucleus-targeted delivery of antitumor agents is of great interest in cancer therapy, since the nucleus is one of the most frequent targets of drug action. Here we report a smart polymeric conjugate platform, which utilizes stimulus-responsive strategies to achieve multistage nuclear drug delivery upon systemic administration. The conjugates composed of a backbone based on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer and detachable nucleus transport sub-units that sensitive to lysosomal enzyme. The sub-units possess a biforked structure with one end conjugated with the model drug, H1 peptide, and the other end conjugated with a novel pH-responsive targeting peptide (R8NLS) that combining the strength of cell penetrating peptide and nuclear localization sequence. The conjugates exhibited prolonged circulation time and excellent tumor homing ability. And the activation of R8NLS in acidic tumor microenvironment facilitated tissue penetration and cellular internalization. Once internalized into the cell, the sub-units were unleashed for nuclear transport through nuclear pore complex. The unique features resulted in 50-fold increase of nuclear drug accumulation relative to the original polymer–drug conjugates in vitro, and excellent in vivo nuclear drug delivery efficiency. Our report provides a strategy in systemic nuclear drug delivery by combining the microenvironment-responsive structure and detachable sub-units.     

Synthetic zeolites as a new tool for drug delivery

Synthetic zeolites were studied in order to investigate their ability to encapsulate and to release drugs. In particular, a zeolite X and a zeolitic product obtained from a cocrystallization of zeolite X and zeolite A were examined. These materials were characterized by chemical analyses (ICP-AES), X-ray diffraction, nitrogen adsorption isotherm, scanning electron microscopy, laser diffraction, and infrared spectroscopy. Since ketoprofen was chosen as a model drug for the formulation of controlled-release dosage forms, it was encapsulated into these two types of synthetic zeolites by a soaking procedure. Drug-loaded matrices were then characterized for entrapped drug amount and thermogravimetric behavior. In both types of activated zeolites, the total amount of ketoprofen (800 mg) was encapsulated in 2 g of matrix. By using HPLC measurements, ketoprofen release studies were done at different pH conditions so as to mimick gastrointestinal fluids. The absence of release in acid conditions and a double phased release, at two different pH values (5 and 6.8), suggest that after activation these materials offer good potential for a modified release delivery system of ketoprofen.     

Superhigh-magnetization nanocarrier as a doxorubicin delivery platform for magnetic targeting therapy

The aim of this study describes the creation of superhigh-magnetization nanocarriers (SHMNCs) comprised of a magnetic Fe(3)O(4) (SHMNPs) core and a shell of aqueous stable self-doped poly[N-(1-one-butyric acid)]aniline (SPAnH), which have a high drug loading capacity (～27.1 wt%) of doxorubicin (DOX). The SHMNCs display superparamagnetic property with a magnetization of 89.7 emu/g greater than that of Resovist (a commercial contrast agent used for magnetic resonance imaging; 73.7 emu/g). Conjugating the anticancer drug DOX to these nanocarriers enhances the drug's thermal stability and maximizes the efficiency with which it is delivered by magnetic targeting (MT) therapy to MGH-U1 bladder cancer cells, in part by avoiding the effects of p-glycoprotein (P-gp) pumps to enhance the intracellular concentration of DOX. The high R2 relaxivity (434.7 mM(-1)s(-1)) of SHMNCs not only be a most effective MT carrier of chemotherapeutic agent but be an excellent contrast agent of MRI, allowing the assessment of the distribution and concentration of DOX in various tissues and organs. This advanced drug delivery system promises to provide more effective MT therapy and tumor treatment using lower therapeutic doses and potentially reducing the side effects of cardiotoxicity caused by DOX.     

Novel approaches to intraperitoneal drug delivery

The prolonged continuous intraperitoneal infusion of cytoarabin was studied in 28 courses. Only 9 courses were completed for the full period of 3 weeks. No cytoarabin was detected in the plasma of patients on any of these courses. The combination of intraperitoneal administration of methotrexate and dipyridamole did not show a synergistic interaction of these 2 substances. However, the addition of dipyridamole to etoposide showed a clear synergy between these 2 substances studied on a human ovarian carcinoma cell line.     

Water-soluble polymers with low critical solution temperature (LCST) as carriers for protein drug delivery

The copolymers of N,N-diethylacrylamide and ovomucoid from duck egg white (an inhibitor of proteolytic enzymes) with low critical solution temperature (LCST) have been synthesized. The behaviour of these copolymers at the point of phase transition was investigated. It was shown that the relation between LCST and physiological activity for these copolymers is a function of their composition. The increase of ovomucoid content leads to the increase of LCST. When the content of ovomucoid rises above 0.2 mol%, LCST disappears. At the same time the physiological activity of obtained copolymers decrease with increasing of N,N-diethylacrylamide content.     

Vitamin E TPGS as a molecular biomaterial for drug delivery

D-α-tocopheryl polyethylene glycol succinate (Vitamin E TPGS, or simply TPGS) is a water-soluble derivative of natural Vitamin E, which is formed by esterification of Vitamin E succinate with polyethylene glycol (PEG). As such, it has advantages of PEG and Vitamin E in application of various nanocarriers for drug delivery, including extending the half-life of the drug in plasma and enhancing the cellular uptake of the drug. TPGS has an amphiphilic structure of lipophilic alkyl tail and hydrophilic polar head with a hydrophile/lipophile balance (HLB) value of 13.2 and a relatively low critical micelle concentration (CMC) of 0.02% w/w, which make it to be an ideal molecular biomaterial in developing various drug delivery systems, including prodrugs, micelles, liposomes and nanoparticles, which would be able to realize sustained, controlled and targeted drug delivery as well as to overcome multidrug resistance (MDR) and to promote oral drug delivery as an inhibitor of P-glycoprotein (P-gp). In this review, we briefly discuss its physicochemical and pharmaceutical properties and its wide applications in composition of the various nanocarriers for drug delivery, which we call TPGS-based drug delivery systems.     

Synthesis and characterization of dendritic star-shaped zwitterionic polymers as novel anticancer drug delivery carriers

In this work, a novel dendritic star-shaped zwitterionic polymer, polyamidoamine-graft-poly[3-dimethyl (methacryloyloxyethyl) ammonium propanesulfonate] (PAMAM-g-PDMAPS), was synthesized. PAMAM dendrimers (generation 2, G2) were firstly prepared and then converted into the PAMAM-Br macroinitiator with 2-bromoisobutyryl bromide for ATRP. Finally, ATRP of zwitterionic DMAPS was carried out to obtain the dendritic star-shaped polymers PAMAM-g-PDMAPS with different PDMAPS chain lengths. Fourier transform-infrared spectroscopy, ¹H?NMR, dynamic laser light scattering (DLS), and TEM were used to characterize the polymers. Encapsulation of adriamycin (ADR) by PAMAM-g-PDMAPS nanoparticles and ADR release behavior from ADR-loaded PAMAM-g-PDMAPS nanoparticles were investigated in detail. PAMAM-g-PDMAPS polymers, even starting from low-generation PAMAM core (G2), were found to show high loading efficiency for ADR because ADR existed not only within G2 PAMAM cores but also in PDMAPS layers. The release profile of ADR from ADR-loaded PAMAM-g-PDMAPS nanoparticles was pH-sensitive and could be controlled by the length of PDMAPS chains. Cell viability studies indicated that ADR-loaded PAMAM-g-PDMAPS could effectively restrain the growth of HepG2 cells and even kill them, whereas PAMAM-g-PDMAPS exhibited nontoxicity. All these results demonstrated that dendritic star-shaped zwitterionic polymers PAMAM-g-PDMAPS are attractive candidates as anticancer drug delivery carriers.